Why did I get an "Expected Route Not Provided" notice when filing with a Civil Air Patrol callsign?

If you file a flight plan with a Civil Air Patrol (CAP) callsign, you will not receive expected route information in your Expected Route Notification email. This is because the FAA doesn't include any military flights in their feed. The CAP is quasi-military and an adjunct to the US Air Force.

Even filing the N-number of your CAP aircraft may not yield an expected route if the N-number is recorded as belonging to a military aircraft.